Ceramic filter using multiple thin piezoelectric layers

Abstract

A ceramic filter including a piezoelectric ceramic and input and output electrode groups disposed within the ceramic body. The input electrode group and the output electrode group extend toward each other from opposing sides of the piezoelectric ceramic. They do not meet, however, and a predetermined spacing, along the thickness dimension of the ceramic, separates the two electrode groups. The input and output electrode groups are each composed of a plurality of electrodes which overlap each other with ceramic layers interposed therebetween.

What is claimed is: 
     
       1. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness, said ceramic being polarized in one direction along a direction corresponding to said thickness;   bulk wave eliminating means for eliminating bulk waves which produce spurious vibrations other than utilizable bulk waves located at, at least one of said first and second ends of said ceramic;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart, alternate internal electrodes which follow one another in each said input and output electrode groups being led out to respective first and second lateral sides of said piezoelectric ceramic;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second lateral sides, and a second pair of external electrodes having first and second external contacts for contacting, respectively, said output internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       2. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness; said multi-layered piezoelectric ceramic being polarized in one direction along a direction corresponding to said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart, alternate internal electrodes which follow one another in each said input and output electrode groups being led out to respective first and second lateral sides of said piezoelectric ceramic;   at least one of said input and output electrode groups comprising first and second excitation parts spaced nλ+λ/4 apart in the direction of said thickness of said multi-layered piezoelectric ceramic;   bulk wave direction control means for enabling bulk waves produced by said first excitation part to propagate in a direction opposite to said second excitation part;   a first pair of external electrodes having a first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second lateral sides, and a second pair of external electrodes having first and second external contacts for contacting, respectively, said output internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       3. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness; said multi-layered piezoelectric ceramic being polarized in one direction along a direction corresponding to said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart, alternate internal electrodes which follow one another in each said input and output electrode groups being led out to respective first and second lateral sides of said piezoelectric ceramic, at least one of said input and output electrode groups being weighted;   a first pair of external electrodes having a first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second lateral sides, and a second pair of external electrodes having first and second external contacts for contacting, respectively, said output internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       4. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart;   alternate ones of said plurality of ceramic sheets on which said internal electrodes are formed being oppositely polarized along the direction of said thickness, alternate internal electrodes which follow one another in each said input and output electrode groups being led out respectively to respective first and second lateral sides of said ceramic body;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting, respectively, said output internal electrodes which are led out at said first and second sides;   bulk wave eliminating means for eliminating bulk waves which produce spurious vibrations other than utilizable bulk waves located at, at least one of said first and second ends of said ceramic; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       5. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart;   at least one of said input and output electrode groups including first and second excitation parts spaced nλ+λ/4 apart from each other in the direction of said thickness of said multilayer piezoelectric ceramic;   bulk wave direction controlling means for enabling bulk waves produced by said first excitation part to propagate only in a direction opposite to said second excitation part;   alternate ones of said plurality of ceramic sheets on which said internal electrodes are formed being oppositely polarized along the direction of said thickness, alternate internal electrodes which follow one another in each said input and output electrode groups being led out respectively to respective first and second lateral sides of said ceramic body;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting, respectively, said output internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       6. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart, at least one of said input and output electrode groups being weighted;   alternate ones of said plurality of ceramic sheets on which said internal electrodes are formed being oppositely polarized along the direction of said thickness, alternate internal electrodes which follow one another in each said input and output electrode groups being led out respectively to respective first and second lateral sides of said ceramic body;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting, respectively, said output internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       7. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart;   each of said plurality of internal electrodes of said input and output electrode groups comprising a plurality of divisional electrodes having first and second adjoining electrodes at least partly opposed to a third electrode which adjoins said first and second electrodes through a ceramic layer, whereby a successive connection of said first electrode, piezoelectric ceramic layer, third electrode, piezoelectric layer, and the second electrode produces a series-connected capacitor forming portion;   said piezoelectric ceramic layers being polarized in the direction of said thickness, a portion of a given ceramic layer positioned between said first and third electrodes being polarized in an opposite direction from a portion positioned between said second and third electrodes;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       8. A ceramic filter as in claim 7, wherein said filter includes a first ceramic layer positioned adjacent said first end and a second ceramic layer positioned adjacent said second end and wherein the thickness of said first and second layers is selected to produce a predetermined center frequency. 
     
     
       9. A ceramic filter as in claim 7, wherein at least one of said internal electrodes of said input electrode group, is formed on said first end of said ceramic and at least one of said output internal electrodes is formed on said second end. 
     
     
       10. A ceramic filter as in claim 7, further comprising at, at least one of said first and second ends of said ceramic bulk wave eliminating means for eliminating bulk waves which produce spurious vibrations other than utilizable bulk waves. 
     
     
       11. A ceramic filter as in claim 7, wherein at least one of said input and output electrode groups comprises first and second excitation parts spaced nλ+λ/4 apart in the direction of said thickness of said multilayered piezoelectric ceramic, said filter further comprising bulk wave direction control means for enabling bulk waves produced by said first excitation part to propagate only in a direction opposite to said second excitation part. 
     
     
       12. A ceramic filter as in claim 7, wherein at least one of said input and output electrode groups is weighted. 
     
     
       13. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness, said piezoelectric ceramic being polarized in a direction at right angles to the direction of said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart;   alternate internal electrodes which follow one another in each said input and output electrode groups being led out respectively to respective first and second lateral sides of said piezoelectric ceramic;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting respectively said output internal electrodes which are led out at said first and second sides;   bulk wave eliminating means for eliminating bulk waves which produce spurious vibrations other than utilizable bulk waves located at, at least one of said first and second ends of said ceramic; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       14. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness, said piezoelectric ceramic being polarized in a direction at right angles to the direction of said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart;   at least one of said input and output electrode groups comprising first and second excitation parts spaced nλ+λ/4 apart in the direction of said thickness of said multi-layered piezoelectric ceramic;   bulk wave direction control mans for enabling bulk waves produced by said first excitation part to propagate in a direction opposite to said second excitation part;   alternate internal electrodes which follow one another in each said input and output electrode groups being led out respectively to respective first and second lateral sides of said piezoelectric ceramic;   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting respectively said output internal electrodes which are led out at said first and second sides; and   means for applying a voltage to at least one of said input electrodes and producing an output at said output electrode group in response to vibrations which propagate from said input group to said output group.   
     
     
       15. A ceramic filter comprising: a multi-layered piezoelectric ceramic body including a plurality of stacked ceramic sheets, said ceramic body having a thickness extending through said plurality of stacked sheets and first and second opposite ends separated along said thickness, said piezoelectric ceramic being polarized in a direction at right angles to the direction of said thickness;   an input electrode group including a plurality of internal input electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said first end of said ceramic body, adjacent ones of said input electrodes overlapping each other along said thickness of said ceramic body;   an output electrode group including a plurality of internal output electrodes, at least one electrode being formed on each sheet of a selected group of said sheets lying adjacent said second end of said ceramic body, adjacent ones of said output electrodes overlapping each other along said thickness of said ceramic body, said input and output groups overlapping each other along said thickness and being spaced a predetermined distance apart;   alternate internal electrodes which follow one another in each said input and output electrode groups being led out respectively to respective first and second lateral sides of said piezoelectric ceramic, said alternate internal electrodes comprising alternate cavities which extend to the respective first and second lateral sides of said ceramic, and which are filled with molten metal after polarization; and   a first pair of external electrodes having first and second external contacts for contacting, respectively, said input internal electrodes which are led out at said first and second sides and a second pair of external electrodes having first and second external contacts for contacting respectively said output internal electrodes which are led out at said first and second sides.   
     
     
       16. A method for forming cavities for a ceramic filter as in claim 15, the method including the steps of applying carbon paste to portions of ceramic green sheets where electrodes are to be formed, laminating the ceramic green sheets, and sintering the laminated ceramic green sheets so that the carbon burns out and said cavities are formed at positions where the layers of carbons were present. 
     
     
       17. A ceramic filter as in claim 15, further comprising at, at least one of said first and second ends of said ceramic bulk wave eliminating means for eliminating bulk waves which produce spurious vibrations other than utilizable bulk waves. 
     
     
       18. A ceramic filter as in claim 15, wherein at least one of said input and output electrode groups comprises first and second excitation parts spaced nλ+λ/4 apart in the direction of said thickness of said multi-layered piezoelectric ceramic, said filter further comprising bulk wave direction control means for enabling bulk waves produced by said first excitation part to propagate in a direction opposite to said second excitation part. 
     
     
       19. A ceramic filter as in claim 15, wherein at least one of said input and output electrode groups is weighted. 
     
     
       20. A ceramic filter as in claim 1, 4, 10, or 13, wherein said means for eliminating bulk waves comprises a plurality of grooves defined at least in one of said first and second ends of said ceramic, said grooves extending along the direction of said thickness of said ceramic and having a groove depth which is defined by the relation 2d=(n+1/2)λ wherein n is the number of electrodes, λ is the wave length of the bulk waves and d is the groove depth. 
     
     
       21. A ceramic filter as in claim 1, 4, 18, or 13, wherein said means for eliminating bulk waves comprises an inclined surface defined at least one of said first and second ends of said ceramic. 
     
     
       22. A ceramic filter as in claim 1, 4, 18 or 13, wherein said means for eliminating bulk waves comprises a spherical surface defined along at least one of said first and second ends. 
     
     
       23. A ceramic filter as in claim 3, 6, or 20, wherein said at least one input and output electrode groups is weighted by successively increasing the overlap between adjacent ones of said plurality of internal electrodes from said first and second ends of said ceramic toward the center of said ceramic body.